104 GENETICS 



7. DEFINITIONS 



A character which is present in the offspring in 

 double quantity because it was present in both parents 

 is said by Bateson to be homozygous, while an or-' 

 ganism which is homozygous with respect to any char- 



D (Dominant) 



DD DD DD. 2D(R) RR RR RR 

 FIG. 17. General Mendelian formula for a monohybrid. 



,-> 



acter is called a homozygote so far as that particular 

 character is concerned (DD or RR.) 



In contrast to the homozygous condition, an organ- 

 ism is said to be heterozygous when it derives the deter- 

 miner of a character from only one parent. Such 

 an organism is described as a heterozygote with respect 

 to the character in question (DR). 



Organisms that appear to be alike, regardless of 

 their germinal constitution, are said by Johannsen to 

 be identical phenotyjpically (DD and DR), while or- 

 ganisms having identical germinal determiners- are 

 said to be genotypically alike (DD and DD or RR 

 and RR). 



